JP2012516796A - Process of micro-foam injection molding for personal consumer care products and their containers - Google Patents

Abstract

To solve various problems of materials of general consumer goods and care products.
An injection molding process produces a microcellular material. In this method, the polymer is dissolved and mixed with a supercritical fluid to produce a single phase polymer gas solution. This solution is injected into the mold through a nozzle. When injected through the nozzle, the gas in the solution (from the supercritical fluid) emerges from the polymer. It then solidifies. In emerging from solution, the gas results in nucleated bubbles resulting in a microbubble structure. The foam material includes a polymer having a structure of fine bubbles generated by nucleation of fine bubbles. Microbubbles are created by sprinkling supercritical fluid into a polymer solution. At that time, the polymer is subjected to a pressure drop. Feminine hygiene products are made from foamed polymers.
[Selection] Figure 1

Description

  The present invention relates generally to personal consumer care products, and more narrowly to personal consumer care products and methods of making microfoamed plastic foams for use in containers thereof.

  Many personal consumer care products and their containers are made from plastic. Most plastics are thermoplastic materials. When the thermoplastic substance is heated in a solid state, it melts and becomes a fluid, and is cooled again and solidifies. This process can be repeated. On the other hand, some plastics are thermosetting and react at high temperatures and pressures to cross-link into solids. The term “crosslink” means that two chains of a polymer are connected by a bridge formed by an element, group, or composition. These elements, groups, or compounds join one chain of carbon molecules to another chain of carbon molecules through a basic chemical link to form a cross-linked network.

  Methods for treating any of these types of plastics, especially thermoplastics, to make personal consumer care products and their containers include injection molding, blow molding, extrusion molding, thermoforming, and the like. . Although such processes are widely used, currently these processes and the products made by these processes still have drawbacks. For example, by using complex molds, high quality injection molded products can be produced in large quantities and at high speed, but the price of the resin is particularly high for disposable items. Recently, as the price of crude oil has soared, the price of resin has already increased considerably and is expected to be higher in the future. It is desirable to directly reduce the total amount of both raw materials and processing in order to ultimately reduce the total cost incurred by the consumer. It also helps to reduce the amount of plastic waste in products and containers that are discarded into the surrounding environment.

  However, there is a limit to reducing the amount of such resin used. Mechanical properties that indicate the structural integrity of a product (such as modulus, hardness, impact strength) are generally considered to be reliable if the thickness (and weight) of a part decreases beyond a predetermined threshold. Loses sex. Thus, the products are sized to accommodate and withstand the typical forces and pressures to which they are exposed. These forces and pressures occur during the final use, handling, or transportation stages of the supply chain. Very light products can bend, tear or otherwise deform under these forces and stresses.

  The weight of a particular part can be reduced (and therefore the amount of resin can be reduced) by adding gas to produce a “foam” part consisting of air and resin. For example, the “gas-assisted” injection molding process introduces gas into a material heated to a high temperature. By introducing gas into the hot material, the resin material is replaced and the volume of the material increases. This allows certain parts to have reduced amounts of resin (and lower weight) and lower costs while maintaining mechanical properties.

  Unfortunately, however, gas-assisted injection molding involves other expensive processes, and for thick-walled parts, thick-walled embedded parts that allow gas flow paths to be formed, etc. Its use is limited. More particularly, the performance of gas-assisted injection molding and the associated manufacturing accuracy are generally inferior to making thin walled parts that contain a hollow volume containing air or other filling gas. It is enough. Often, parts used in personal consumer care products have a thin wall shape. For example, petals used on tampon applicators are generally very thin. And a thickness of about 0.010 inches or less is preferred to allow the tampon pledget to be removed with minimal force. It is very difficult to cut through such a small channel in a thin-walled petal, and control of the air space of a minimum level size is required. Therefore, even with finely designed molds and optimized processes, problems can arise with regard to high part quality, reproducible part dimensions, minimum part warpage and shrinkage.

  In one aspect, the present invention provides a method of injection molding. The method produces minute materials that can be built into various thin wall structures such as feminine hygiene products. In this method, the polymer is dissolved and mixed by a supercritical fluid to produce a single phase polymer gas solution. The single phase polymer gas solution is then injected into the mold through a nozzle. When injected through the nozzle, gas (from supercritical fluid) in the polymer solution emerges from the polymer solution and polymer solids. In emerging from the polymer solution, the gas facilitates nucleation and subsequent bubble growth to produce a fine foam structure. The single phase polymer gas solution is maintained at a temperature even higher than about 20 degrees Celsius above the melting point of the ordered polymer or plastic. It is after adding supercritical fluid and before injecting a single phase polymer gas solution through the nozzle.

  In another aspect, the present invention provides a foam material. The foam material consists of a polymer having a fine foam structure that is foamed by nucleation and subsequent bubble growth. The microbubbles are foamed by diffusing supercritical fluid into the polymer solution. That is when the polymer in the liquid state is subjected to conditions of thermodynamic instability such as the sudden pressure drop that occurs during injection molding.

  In another aspect, the present invention provides feminine hygiene products made from foamed polymers. The polymer has a microfoamed structure produced from a polymer in a dissolved state by diffusing a supercritical fluid. The polymer is dissolved when the polymer is solid.

  In another aspect, the present invention provides a method for injection molding of feminine hygiene products. In this method, the basic polymer is supplied to the extrusion device in the form of small particles, for example, through a hopper. The underlying polymer may include a thermoplastic resin and at least one other additive such as a colorant, lubricant, slip agent, processing aid, and the like. Supercritical fluid is also added to the extrusion device. Then, the basic polymer and the gas exceeding the criticality are mixed. This combination is then injected into a mold to provide a feminine hygiene product. As a result, the sanitary product has a substantially continuous thermoplastic matrix phase.

  One advantage is that supercritical fluids help to plasticize the resin. Thereby, the overall viscosity of the mixture of resin and supercritical fluid is reduced (and also its transition temperature is reduced), and thus when each part is made using the method according to the present invention, Manufacturable at low temperature and low pressure compared to the process of technology. Lower temperatures and viscosities result in higher productivity. Because (1) the mixture is injected with less heat to be eliminated at a lower temperature and at a viscosity low enough to fill the cavity. As a result, the cooling time required to eliminate a smaller amount of heat is reduced. (2) Gas is generated and diffused from the mixture. The resin then acquires its transition temperature, thereby allowing the material to quickly become glassy (and hence hard). Furthermore, nucleation and bubble growth of the mixture effectively fills the mold. As a result, the cycle time used to fill the mold is reduced or unnecessary. In addition, the time to cool the part is reduced. Not only because the temperature difference between the cold mold and the warm part is reduced, but also because the nucleation and growth of bubbles is a process of endothermic reaction.

  Another advantage of the process is that it can be used for a very large number of different types of polymer resins. While most of the conventional technologies have been concentrated on polyamide, the micro-bubble foaming process can be applied to polyethylene, polypropylene, polycarbonate, polystyrene, rubber and the like.

  Another advantage is that the process significantly reduces the weight of each manufactured part. That means that the parts to be manufactured are transported more economically, i.e. their costs can be saved by reducing the material. Furthermore, less material means that the cycle time is reduced. On the other hand, the aesthetic and mechanical properties of each manufactured part are comparable to that of parts manufactured by the prior art and more expensive processing processes. The amount of weight loss in the parts produced by the process according to the present invention (compared to the process of conventional injection molding) is generally about 0.5 percent or more and about 30 percent or less, preferably about 10 Greater than or equal to about 20 percent.

FIG. 1 is a schematic view showing an apparatus for performing a processing process of fine foam injection molding according to the present invention. FIG. 2 is a diagram showing an image of a foamed polymer having data read by a scanning electron microscope (SEM). FIG. 3 is an SEM image representing the bubble morphology of a sample of microfoamed low density polyethylene (LDPE) produced at an intermediate fuselage temperature. FIG. 4 is an SEM image representing the bubble morphology of a micro-foamed LDPE sample produced at high fuselage temperatures. FIG. 5 is a photograph showing two extensible bars. FIG. 6 is an enlarged view of an SEM image representing the form of bubbles in the LDPE sample. FIG. 7 shows the surface of a part injection molded in accordance with the prior art, loaded with data using a Zygo (trademark) optical profiling system (available from Zigo, Middlefield, Connecticut). It is an image showing a shape. FIG. 8 shows the surface of a part formed by micro-foaming injection molding using a Zygo (trademark) optical profiling system that can be purchased from Zigo, Middlefield, Connecticut. It is an image showing a shape. FIG. 9 is a diagram illustrating a computer screen image in the computer simulation. FIG. 10 is a schematic diagram of an experiment performed using the computer simulation of FIG. FIG. 11 shows a photograph of several adjacent extensible rods obtained from the microfoam injection molding process (150 micron Teflon coated on the mold). is there. FIG. 12 shows a photograph of several adjacent extensible rods obtained from a micro-foam injection molding process (75 micron Teflon coated on the mold). is there. FIG. 13 is a side view of the end of the petal of the body portion of the formed tampon applicator. FIG. 14 is a cross-sectional view of a mold for a portion of a torso part of a tampon applicator that is gripped by a user with a finger. FIG. 15 is a view showing a photograph of the body surface of the tampon applicator formed by the processing process according to the present invention. FIG. 16 is an enlarged image of the body surface of the tampon applicator according to FIG. FIG. 17 is a view showing a photograph of a petal of a body portion of a tampon applicator formed by the processing process according to the present invention. FIG. 18 is a view showing an optical micrograph of the shape of a part gripped by the user of the body of the tampon applicator body formed by the processing process according to the present invention.

  In one embodiment of the invention, the micro-foam injection molding process uses a fluid that exceeds one or more criticalities to produce a foamed part. In this process, an atmosphere gas (usually nitrogen or carbon dioxide) in a supercritical state is mixed with the resin. As used herein, the term “resin” means a polymer resulting from a chemical reaction between two or more substances. The terms “resin” and “polymer” are used interchangeably below. In the present invention, the gas is mixed with a polymer melt inside the machine fuselage to produce a single phase polymer gas solution. The single phase polymer gas solution is injected into the mold through a nozzle. Thus, the polymer becomes a solid. When injected through the nozzle, a sudden drop in pressure occurs, causing gas to emerge from the polymer melt, resulting in a large number (typically about 1 to about 1 billion nuclei per cubic centimeter of plastic). The resulting “microbubble” nuclei. As used below, the term “exceeding criticality” with respect to a fluid means the highest pressure and temperature at which the liquid is not capable of transitioning to vapor.

  The process of microfoam injection molding according to the present invention can be used to produce various foamed parts. Such parts include, but are not limited to, parts for personal consumer care products and their containers. In particular, molds and moldings for specific foamed parts have traditional injection molding designs and suitable microbubble foaming treatments to make improved mold parts. Provides basic principles for rapidly and rationally developing processes. Products in which the microfoam injection molding process of the present invention can be utilized include, but are not limited to, feminine hygiene products such as tampon applicators and containers for such instruments.

  The resins that can be used in the process of the present invention have essentially either thermoplastic or thermosetting properties. Due to their nature, thermoplastic resins are suitable for being repeatedly heated, melted, cured and redissolved. That allows the equipment in which they are incorporated to be recycled.

  However, the use of thermosetting resins is not preferred due to cross-linking. Thermosetting resins typically tend to suppress repeated heating, dissolution, and coagulation that are characteristic of thermoplastic resins. When a thermosetting resin is heated, the material generally does not become as soft as a thermoplastic resin. This is because thermosetting resins have a cross-linked network. If an excessive amount of heat is applied to the thermosetting resin, the cross-linked structure can burn and break. Therefore, thermosetting resin materials generally cannot be re-melted or re-cured after they are cross-bonded and cured. Moreover, thermosetting resins are not very familiar with injection molding according to the present invention, suitable for instruments, composites, and processes suitable for extrusion.

  One of the resins that can be used in this process is low density polyethylene (LDPE) having a concentration of at least about 70 percent and preferably at least about 80 percent. However, the present invention is not limited to this, and other resins may be used. On the other hand, LDPE is currently preferred. This is because the cost is low, the molding is easy, and it has appropriate mechanical properties. LDPE exhibits an excellent coefficient of friction when used in combination with Tampon and other feminine hygiene products. In particular, it is easy and comfortable when inserting a tampon applicator. Other resins that can be used are polyamides, polypropylene, other polyolefins, polyolefins and other thermoplastics, polycarbonates, polystyrene, rubber, polylactides, polyalkanoates, mixtures of the above-mentioned resin types, terpolymers , And a mixture of thermoplastic and starch-based resins. A mixture of polylactide, polyalkanoate, and thermoplastic starch-based resin is renewable (sustainable) and can be washed away and / or decomposed into organic matter, Therefore, it may show a minimal environmental impact in the waste stream.

  One supercritical fluid that can be used as an atmospheric gas is nitrogen. Nitrogen is relatively inert and is believed to exhibit good solubility and reasonably high diffusivity among many resins. Nitrogen also has supercritical properties at relatively low pressures and temperatures. For example, the critical temperature of nitrogen is 126.2 Kelvin degrees and its critical pressure is 3.39 megapascals. Furthermore, nitrogen is currently cheap and can be obtained very easily. In one exemplary process of the present invention, the supercritical fluid nitrogen loading is greater than or equal to about 0.04 weight percent and less than or equal to about 1 weight percent, greater than or equal to 0.05 weight percent, and greater than or equal to about 0.0. 45 weight percent or less is preferred, with 0.1 weight percent or more and about 0.35 weight percent or less being most preferred. Other supercritical fluids that can be used in the process are carbon dioxide, a mixture of nitrogen and carbon dioxide, but are not limited thereto.

  Regardless of whether the supercritical fluid is nitrogen, carbon dioxide, or some other gas, the use of supercritical fluid in the presence of gas is Allows for more accurate dosing of fluids beyond the criticality and good solubility. Bubbles generated by the nuclei thus grow in a predictable and controllable manner, reducing the weight of the part with minimal sacrifice of mechanical properties or part aesthetics. Compared to gas-assisted injection molding, this process is different in that it makes it possible to produce fine bubbles. The microbubbles are micro-sized cavities and can be present on walls as thin as 0.01 inches. The mechanical properties of the final part are directly affected by the bubble size, bubble density, and homogeneity of the bubble structure. They are all controllable.

  Various additives are incorporated into the resin during the process of microfoam injection molding. Such additives include colorants (eg, ultramarine blue, clinakidon violet), pigments (eg, Pigment Yellow 180, Pigment Green 7 etc.), and opacifiers (eg, titanium dioxide), It is not limited. They are used to obtain the color preferred by the final user. Pearl-like pigments (pearly materials) and / or mica may also be added to enhance aesthetic quality. Antioxidants such as hindered phenols (eg butylated hydroxytoluene, Irganox (Ciba) 1010, Irganox 29, etc.) and dilauryl thiodipropionate are used in high temperature processing and heat. May be used to aid in mechanical stability. Flame retardants may also be added. Lubricants, pigment dispersants, and / or other processing-promoting substances such as zinc stearate, erucamide, ethylene bis stearamide, etc. (eg, chemicals for demolding) are also added. May improve the lubricity and / or aesthetics of the material being molded. In particular, with respect to feminine hygiene products, the problem is that the products are easily and comfortably inserted. Inorganic fillers such as calcium, carbonate, etc. can also be added to reduce overall costs and provide strength. Impact modifiers and / or thermoplastic elastomers may also be added to improve impact properties and / or flexibility / elasticity.

  In addition, other additives may be incorporated into the resin to improve and optimize the microfoam injection molding process. In particular, nanometer-sized clay particles may be added to the resin. These particles not only serve to promote bubble nucleation, but also produce nano-level composite bubbles with small renewable bubble sizes. The combination of the exfoliating effect of clay and its interfacial properties generally tends to promote bubble nucleation and reduce the growth rate. This results in small, uniformly sized “micro bubbles” in the foam that are well diffused. It provides enhanced product properties in the overall process of more stable microbubbles and low part weight. The resulting microbubbles have a diameter of about 1 micron or more and about 200 microns or less, more preferably about 3 microns or more and about 20 microns. The total amount of nanometer-sized clay particles added to the resin is up to about 10 weight percent, preferably 3 to 5 weight percent.

  The present invention is not limited to including the above-mentioned additives, and others not described may be used. All additives incorporated into the process are combined together in a bundle (also known as “color concentrate”). It is then added together to the resin to provide the desired balance of aesthetic and mechanical properties.

  Resin blends or special grades may also be useful in connection with the present invention. The use of alternative resins or resin blends may provide advantages. It may or may not be related. The first advantage is related to viscosity and the second advantage is related to interface properties. Both tend to improve the surface quality and / or other characteristics of the molded part. Regarding the advantage of viscosity, the supercritical fluid used in the present invention has a low viscosity, so that it can act as a plasticizer to lower the overall viscosity. The use or mixing of resins having a lower viscosity than those used in conventional injection molding is therefore sensible. The mold fills faster and the viscosity more closely matches that of the supercritical fluid. Regarding the benefits of interfacial properties, the use of alternative resins or resin mixtures may have the benefit of interfacial energy. For example, adding a small amount of polypropylene to LDPE has been found to lower both the free energy barrier to nucleation and the interfacial energy of the resin to the growth of microbubbles generated in the process of microbubble foaming. I came. Adding polypropylene to LDPE can also reduce the strength by changing the crystallinity of LDPE. It can greatly affect the foamability of fine bubbles. By closely matching the interfacial energy between the bubble and the resin, the microbubbles are easier to move rather than move to the surface so that the melted tip advances and results in surface imperfections. To produce smooth and aesthetically pleasing parts.

  Making the molding temperature slightly lower than that used in the conventional injection molding process also provides several advantages. In particular, lowering the temperature facilitates a more advantageous interfacial energy balance. Also, the lower viscosity provided by the microbubble foam molding process allows molding of parts at slightly lower temperatures. That improves energy efficiency over that of conventional higher temperature injection molding.

  Applying a thin layer or coating of insulating material such as polytetrafluoroethylene (PTFE) to the mold wall is useful to improve the surface quality of the parts made by the process disclosed below. Is known to be In particular, surface defects such as vortices are reduced or eliminated when the temperature of the polymer on the mold wall is higher than the crystallization temperature of the polymer. More specifically, a 150 micron coating of a fluoropolymer such as PTFE or perfluoroalkoxyl PFA TEFLON (hereinafter PFA) is applied over a thin (eg, about 3.2 millimeters) mold. This results in a substantially uniform type of temperature that achieves this result. In fact, subsequent experiments and analyzes have shown that surface quality problems are eliminated if the temperature is higher than the crystallinity at the mold wall while filling the mold. That was achieved by applying a thin layer of PTFE to the mold walls.

  Furthermore, it has also been found that the surface finish of the mold wall affects the final part surface finish to a much greater extent compared to conventional injection molds. For this reason, improving the finish of the mold, eg, polishing, may also surprisingly improve the surface finish of the final molded part. Strengthening the surface in this way (by polishing the surface instead of using a matte finish) causes the surface to behave differently with respect to the process of the present invention compared to the process of conventional injection molding. Bring that to do.

  The temperature at which the processing process of the fine foam injection molding according to the present invention is performed depends on the resin used. However, in general, the temperature at which the process is performed is about 10 to 50 degrees Celsius lower than that used in conventional injection molding processes. The actual molding temperature can be as high as 10-60 degrees Celsius above the melting point of the polymer, depending on the product and mold design. The preferred decrease in temperature (relative to conventional molds) is on the order of 5-25 degrees Celsius. In one embodiment of the present invention, the process of molding the body of the tampon applicator in the microfoam injection molding according to the present invention is performed at 217 degrees Celsius. For reference, high speed molding of the LDPE based tampon applicator fuselage is typically performed at 224 degrees Celsius. At this temperature, increased nucleation is expected to result from lower surface tension. This is because the activation energy barrier against bubble nucleation is reduced.

  Without wishing to be bound by any particular theory, lowering the temperature will cause the presence of supercritical fluid to be injected compared to the resin composition in the absence of supercritical fluid injection. It is assumed that it is possible to reduce the viscosity of the lysate that is made. It thereby allows operation at lower temperatures and improved heat transfer coefficient. However, there are limits to the lower temperature limits for this operation. This is because, in some respects, the viscosity of the lysate is so high that it cannot be controlled. Performing the process at temperatures around 190 degrees Celsius or higher tends to result in more bubble nucleation than at lower temperatures. This is because an increase in nucleation is expected to result from lower surface tension. This reduces the activation energy barrier to bubble nucleation. The bubble size of the generated bubbles is about 1 micron or more and about 200 microns or less, preferably about 3 microns or more and about 20 microns or less.

  On the other hand, very high molding temperatures can result in weak melt strength. It is that bubbles quickly coalesce the nuclei and form extremely large bubbles (“macro bubbles”). Undesirable surface features such as swirls and rough textures are then introduced. These problems eventually result in weak dimensional stability, undesirable aesthetic appearance, and poor color uniformity.

  The cycle times for the microfoam injection molding process according to the present invention are the time to open and close the mold, the time to fill, the time to pack, the time to cool, and the time to eject the part. The time for various device movements, such as the time associated with the shut-off gate in the runner system into which the resin is injected, is similar to the time for nozzle recapture and also the overall cycle time (open the mold May affect the time it takes to eject the part. In the molding process, these cycle times are relatively short (compared to the conventional molding process). It is for high volume foam products that can be discarded, such as the body of a tampon applicator. The cycle time is short for at least two reasons. First, the time required to form and support the mold is zero. More specifically, the mold is packed as the gas emanates into the growing microbubbles. Therefore, make up for the shrinkage of the material. Second, the heat transfer load is further reduced. Based on these reasons, foamed products (such as tampon applicator bodies) are manufactured using the process of the present invention with a total molding cycle time of 3 to 100 seconds. A preferred cycle time is 3 to 20 seconds, with a cycle time of 4 to 15 seconds being more preferred. Results from a molded viscosity test performed with a model to predict the viscosity of a mixture of resin and supercritical fluid show that the optimum filling rate (and hence the filling time) for the temperature of interest Used to determine.

  In the process of micro-foam injection molding according to the present invention, the mold parts supported together to form a cavity into which a mixture of resin and supercritical fluid is injected are secured together. In general, because lesser amounts of resin are injected (and low melt viscosity due to the presence of supercritical fluids, and bubble expansion through cavities replacing the typical stuffing phase (Because of the low but uniform pressure resulting from), the fixing pressure used in this process is lower than that required for conventional injection molding. The injection pressure is lower. This is because the fixing pressure is generally dominated by the pressure for injection, not the pressure for packing. The pressure for fixation is generally up to about 50 percent lower than that typically used in conventional injection molding. Most preferably, it is as low as 10 to 30 percent.

  More sophisticated injection molding techniques can also be implemented using the present invention. Such implementations include, but are not limited to, co-injection, multi-element molding, overmolding, and the like. For example, this allows consumer goods to be manufactured. This is because it has different polymers with different surface properties. In one exemplary embodiment, one surface may have a high coefficient of friction, such as for a handle that is easy to grip. On the other hand, other surfaces may be designed to be smoother and lubricious and have a lower coefficient of friction.

  It is preferred to use a hot runner system for molding parts using microbubble foam injection molding. On the other hand, with a hot runner system, fluids that exceed the criticality allow the plastic to “drool”. Or even worse, it can have a tendency to "advance" the plastic into the gate through the hot runner system. Therefore, it is preferable to use a gate valve in the process of hot runner injection molding with foaming of fine bubbles. It is to minimize the effect of “dripping” or “advancing”, thereby obtaining a greater weight reduction with respect to the molded part.

  Other techniques that may be used in connection with the present invention include, but are not limited to, in-mold assembly and in-mold labeling.

  In designing a specific micro-foam injection molding process according to the present invention, the volume of parts required per year is predicted, expected labor, overhead, packaging, materials, expected Used along with the cost of the machine to produce this part volume according to the cycle time, the specific design parameters are calculated. Such design parameters include, but are not limited to, the number of cavities in the mold and the tonnage of the machine. (The tonnage of the machine may be considered in the design parameters because the process of micro-foam injection molding according to the present invention is lower tonnage due to lower fixing pressure. And lower machine tonnage means lower energy consumption values.) Any specific machine design is subject to product requirements and multi-factor modeling. It will depend on other appropriate factors such as whether or not it will be executed. In this manner, once a design and process is selected, cost estimates are determined to evaluate investment criteria such as cost per part requirements and overall cost savings. Computer software is used to perform such calculations.

  In setting the parameters and in designing the appropriate mold and machine for the process according to the present invention, the results for other similar processes are appropriate trials with the process of foaming of microbubbles. And can be used with data obtained from experiments for design. This allows optimization and selection of the optimal combination of all parameters.

  The process of micro-foam injection molding according to the present invention is particularly useful for producing tampon components such as tampon applicator bodies. Tampons are large volume disposable products and any attempt to reduce the environmental impact of such products is welcomed by consumers. The tampon applicator body is regulated and is a high quality class 2 medical device. It is like a thin walled petal that is easy to drain the fibrous tampon pledget, as well as a thicker aesthetically designed grip part that is conductive to being gripped by the user's finger Includes very specific molded features. Also, the tampon applicator fuselage is typically efficient and low cost using a high speed molding process as described below, with numerous cavities that fill rapidly and concurrently. Can be manufactured with. Furthermore, the ability to make parts from environmentally friendly resins such as polylactic acid (PLA) provides additional benefits.

  While the process according to the present invention is particularly suitable for injection molding of a tampon applicator body, the overall process, method and system described below is more extensive, i.e. personal goods and Applicable to a wide variety of injection molded items for consumer goods and packaging. In particular, the injection of micro-bubble foam is regular and disposable shaving device, toothbrush, charger, various kinds of containers, bottle tip caps, toys, tampon applicator plunger (as pusher) Can also be used to manufacture parts for

  Different parameters are used for each of the different products made using the microfoam injection molding process. Comparable process parameters are used for each product, but when changing products, for example when changing from the body of a tampon applicator to another product, certain parameters also need to be adjusted. Might be. For example, some products are made using a single shot injection of material. On the other hand, others are made using a multi-step injection process (also known as overmolding). If a multi-step process is used, the microbubble process can be used in any one or more multi-step steps.

  In addition, other thermoplastic processing methods (eg, film, sheet and tube extraction, bottle blow molding, thermoforming, etc.) to make consumer goods and personal care products and packaging Can be used. These methods also benefit from the process of microbubble foaming and the invention described below. Finally, even foaming of thermoset resin nanocomposites can be used to make high strength, low weight materials used in personal and consumer care products and packaging.

Example 1 Extensive Bar Molding Experiment Standard LDPE resin is blended together with a bundle based on standard green LDPE, such as lubricants, slip agents, colorants, and dispersants. A mixture containing 98.4 percent LDPE balanced with various inerts is produced. This resin formulation was used in the parts that are specimens of all the tests in this example and was known as the LDPE resin mixture. This resin was used in injection molding trials to make parts that were test specimens using the following experimental procedure. That is,
Injection molding machine, Aburg 320S Allrounder 55 tons (Aburg, Newington, Connecticut)
Type: ASTM D638 Stretch Test Bar Cooling temperature is 38 degrees Celsius The unit for injecting supercritical fluid is from Trexel Corporation (Woburn, Mass.)
Nitrogen was used as the supercritical fluid.
The flow rate of nitrogen injection was 0.05 to 0.06 kilogram / hour The time of administration of nitrogen was 1.5 seconds.
The weight percent of fluid that exceeded the criticality was 0.15 to 0.17.
(Controlled by dose size.)
The material was a mixture of LDPE pretex resin.
The cycle time was about 55 seconds.

Referring to FIG. 1, an apparatus for performing the process of micro-foam injection molding according to the present invention is schematically shown, generally designated by the reference numeral 10, and hereinafter referred to as “apparatus 10”. As mentioned. The apparatus 10 includes a screw transmission portion 18, a hopper 16 in which a resin and colorant concentrate is added to the transmission component, and an injection molding portion 12. The screw transmission portion 18 has a plasticizing screw that transfers the resin and colorant concentrate through the inlet of the hopper 16 to the injection molded portion 20 and also includes a feed system 14 for adding supercritical fluid. Have. The back pressure supplied between the screw transmission portion 18 and the injection molded portion 12 is not less than about 80 bar and not more than about 200 bar. The resin and colorant concentrate solution is primarily heated by means of mechanical energy resulting from rotation of the plasticizing screw and any other suitable melt (eg, heat or power from deformation As it travels from the hopper 16 through the transmission section 18 using (heat coming from), it is heated to produce a melt. If supercritical fluid is added through the feed system 14, the resulting lysate will be a single phase polymer gas solution. During the filling stage, a single phase polymer gas solution with supercritical fluid is injected into the mold through the appropriate system of runners and gates. As the solution leaves the transmission portion 18, a rapid pressure decrease results, resulting in a micro-foam injection molded part structure having about 10 ^{6 to} about 10 ⁹ holes per cubic centimeter of material and core. Such microcellular plastic made by this process has a hard skin layer and a foamed central part.

  Several different operating temperature profiles and a mixture of several different shot size LDPE resins were used to obtain the desired reduction in part weight.

  Part-by-part dimensions were determined using an optical comparator (Hawk Monodynascope, Model QC200, available from Vision Engineering, Bedford, NH). A commercially available scanning electron microscope (SEM) (model JSM-6100, available from Joel USA, Peabody, Mass.) Was used to visually analyze the extension parts.

  Table 1 provides data for each part that is the test specimen of this example. Comparable examples are described as C1, C2, and C3. On the other hand, Examples A, B, C, D, and E illustrate the present invention. Sample C best illustrates the invention.

  Table 1 Process, temperature, weight, and weight loss. The molding temperature means a temperature set in the nozzle of the machine.

  For examples B and C2 (operating at the lowest molding temperature), it should be noted that the total amount of bubbles in the extensible rod of the microbubbled part is small. Also, the average bubble size (from electron microscope data) was about 200 micrometers and less than about 300 micrometers in diameter (as seen in FIG. 2, low fuselage temperature (134 degrees Celsius). Degrees) and images taken for 20 cubic centimeter injection shot volumes). Furthermore, only a few bubbles grow in many nucleation sites at low temperature conditions.

  For Examples A and C1 (operating at intermediate molding temperatures), each part injected with microbubbles made under these conditions had fewer bubbles than every other part. It should be noted that the bubble was about 200 micrometers in diameter. It should also be mentioned that the nozzle temperature of 151 degrees Celsius is too low to produce bubbles in the polymer. Only a few bubbles were observed in the SEM graphics (images taken for a fuselage temperature of 154 degrees Celsius and a shot volume of an injection of 20 cubic centimeters as shown in FIG. 3). .

  Examples C, D, E, and C3 operated at the highest molding temperature. Example E represented a 9.6% reduction in weight. For example E, the average bubble size is greater than or equal to about 300 micrometers and less than or equal to about 400 micrometers, which is large compared to other bubbles (particularly when compared to bubbles generated at lower molding temperatures). It should be noted that it was considered a bubble. It is argued as the assumption that the size of these bubbles allows the bubbles to grow as a result of higher melting temperatures due to the low melt strength. In addition, with reference now to FIGS. 2-4, the example of a micro-foam injection molded LDPE made at high molding temperatures has more bubbles than those made at lower fuselage temperatures. That should be described. The observed increase in nucleation should be believed to be the result of lower surface tension. It reduced the activation energy barrier to bubble nucleation.

  As shown in FIG. 5, an actual part 30 molded as Example C and a comparative part molded as Example C3 (no foaming of fine bubbles) were compared. Visually it was possible to compare the actual parts. However, Example C part 30 exhibited a 16 percent weight loss over Example C3 part 32. Example C part 30 also exhibited several spiral patterns that did not exist in Example C3 part 32.

  It should be noted that in the SEM micrograph of Example C (FIG. 6), there are numerous bubbles of size from 10 micrometers to 100 micrometers. FIG. 6 shows a higher magnified image of the bubble morphology of a fine bubble LDPE example produced at a higher fuselage temperature (224 degrees Celsius) and a shot volume of 19 cubic centimeter injection. In Example C under the conditions of these experiments, there were much fewer bubbles than the other conditions. The bubble size was about 5 micrometers or more and about 200 micrometers or less.

  For Example D, a weight reduction of about 21 percent (relative to Example C3) was described. As seen from the SEM photo (FIG. 4), several large gas pockets formed in the LDPE resin when injected. This part of polymer was foamed with large bubbles. In FIG. 4, the high fuselage temperature was 224 degrees Celsius and the injection shot volume was 20 cubic centimeters. Comparable results were obtained with a high fuselage temperature of 224 degrees Celsius and an injection shot volume of 18 cubic centimeters.

  Table 2 provides dimensional analysis for examples produced by the process according to the present invention. The dimensions (ie, length, width, and thickness) in the examples were very consistent and comparable despite the decrease in temperature and part weight. It was found that the dimensions remained consistent when the dimensions were rechecked after a few weeks. The only exception was for the thickness observed at 30 percent from the rear end of the part weight for Example D. The observed increased thickness (0.1401 inch) was likely due to the high coalescence rate of the gas bubbles.

  Table 2 Analysis of processing process, temperature, and dimensions for each part

  Table 3 provides a summary of tensile strength for some samples for comparative reference data example C3. Several mechanical property losses were observed. However, the loss is considered insignificant in terms of the smaller amount of plastic used.

  Table 3 Tensile strength of extensible bars made by a process using a supercritical fluid to produce foamed parts compared to conventional injection molding

  The spiral pattern described above may be the result of an indication of gas flow at the surface of the manufactured part. Surface defects represent one of several problems associated with adopting a process using a supercritical fluid to create a foamed part, such as a spiral. Such spirals appear to be caused by bubbles in the surface that are dragged against the mold wall. With reference to FIGS. 7 and 8, it can be seen that the surface of a conventional injection molded part differs in outline from a microbubble part. FIG. 7 shows a part molded by a conventional method. On the other hand, FIG. 8 shows a part molded using the process of the present invention.

  In one embodiment of the invention, an insulator (eg, Teflon® polytetrafluoroethylene (PTFE) or Teflon® perfluoroalkoxyl copolymer (PFA) is used between the mold wall and the polymer. By maintaining the mold temperature high during injection, the surface quality of the part can be improved. In order to provide an effective improvement in surface quality, simulations were performed using the computer simulation program ANSYS 11.0 (which can be purchased from Ansys, Lebanon, New Hampshire). Using the thermal properties of polyethylene, stainless steel, steel, PFA, and PTFE, temperatures were calculated for PFA and PTFE molds of various thicknesses. FIG. 9 provides one result of such a simulation where the temperature at the wall is about 101 degrees Celsius. The results of these simulations suggested experiments that could be performed to improve the surface properties of extensible rods made using supercritical fluid processing. FIG. 10 shows an overview of the experiments performed.

  As a result of computer simulation experiments, it was found that the surface was surprisingly improved by using 150 micron PTFE on a part thickness of 3.2 millimeters. In particular, it should be mentioned that the spiral indicia has been extinguished or at least surprisingly reduced. However, it should also be noted that even with 75 micron PTFE, some examples continued to show signs of gas flow over the surface. On the other hand, the flow sign has been extinguished for some examples of the same conditions. And despite the generally improved surface, some defects have also been described. FIGS. 11 and 12 show some results for each part made using a mold coated with PTFE. In particular, FIG. 11 shows a rod for tensile and flex testing produced by a supercritical fluid process and using a 150 micron PTFE coating on the mold. And FIG. 12 shows an extensible rod produced using a supercritical fluid process and a 75 micron PTFE coating on the mold.

Example 2 Tampon Applicator Body Experiments A four cavity hot runner molding, which is quite complex, is mechanical for an Aburg 320S injection molding system including a power supply and transmission system as shown in FIG. And connected both electrically. A rounded and rounded nozzle was used to inject LDPE plastic. The electrical area that heats the hot runner manifold was controlled by a temperature controller (available from Gammaflux Corporation of Virginia Steering). The mold was cooled with a cooling system using cooling water with an inflow temperature of 10-22 degrees Celsius. The other parameters were similar to those for the stretchable rod forming already described above.

Some other parameters used to form the tampon applicator include the following: That is,
Core pull option, set to start prior to mold opening and reverted prior to mold closing, part discharge by operating with air flow rate 20-40 cubic centimeters per second Celsius Body temperature of about 210 to 216 degrees (410 to 420 degrees Fahrenheit) and molding temperature 13.0 meters circumferential speed per minute 50 to 100 bar back pressure 10.3 cubic centimeters of nitrogen input Supercritical fluid processing, i.e., transport pressure of supercritical fluid Maintains about 1.4 megapascals higher than the melt pressure in the fuselage to incorporate nitrogen into the molded part 0.3-0.7 Time to inject seconds Second time to pack 0 seconds 6-15 seconds of cooling cycle time Approximately 8 to 10 seconds of total cycle time longer than the cooling time

  The parts produced from the process disclosed below are shown in FIGS. 13 and 14, which depict the complexity with which the part can be produced using this process. In FIG. 13, the rear end of the petal of the body of the tampon applicator is shown. In FIG. 14, the mold for the gripping part of the torso of the tampon applicator (finger grip) is indicated generally by the reference numeral 40. The body of the tampon applicator is indicated by reference numeral 42. Once molded, the tampon applicator body 42 has a raised portion 44 that is lifted for easy grasping by the user.

  The gripping portion 40 and the tampon applicator body 42 are shaped by a period of more than two days. The ratio of the underlying resin to the colorant is 19 to 1 (as in the extensibility bar molding of Example 1).

  In addition to the use of 100 percent LDPE, similar parts were made with a composite of 95 percent LDPE with a balance of PTFE (ie, MP-1600 grade Teflon). This complex is an E. coli strain of Wilmington, Delaware. I. Offered by DuPont. In particular, one part was manufactured for feminine hygiene appliances using a mixture of 95.5 percent LDPE, 3 percent green colorant, and 1.5 percent oleamide. This part exhibited a 6.4 percent weight loss over other parts due to the microfoam injection molding process according to the present invention, indicating improved surface quality.

  At least some parts were made without colorants.

  Examples were collected and tested to provide an illustration of the supercritical fluid processing process of the present invention for molding. Processes of fluids that exceeded criticality were labeled as E1, E2, E3, and E4. Comparable examples are produced by a conventional injection molding process and denoted as C4 and C5. Examples are described in Table 4 below.

  Table 4 Example description for molded tampon applicator fuselage

* 95 percent LDPE + (5 percent) (0.73 LDPE) = 98.65 percent LDPE (actual amount), 1.35 percent colorant and other additives.

  The results obtained in these tests are also compared to a comparable tampon applicator fuselage (hereinafter referred to as C6) obtained from a large scale conventional and commodity production scale injection molding machine. It was done.

  Some molding tests were also performed using a small percentage of nano-level particle mixing.

The following results were described. That is,
Due to slight processing differences, the C4 comparative reference data part weighed about 5 percent compared to the C6 part.
The E1 part weighed about 5 percent less than the C4 part.
Petals produced by the process of supercritical fluid did not produce any flushing. And no problem was described (eg, there was no problem with closing the petal in the tampon applicator).
Minor differences in surface quality have been described. In particular, the surface of the fuselage for the supercritical fluid processing part (E1-E4) was rougher than for the comparative part (C4-C6). There was little difference for parts made with 5 percent PTFE. There was little difference, especially for the examples carried out with shorter cooling times.
It has been found that dimensional stability over time is adequate.

  Table 5 below summarizes the measured weights and dimensions of the C4 example for E1. Some differences may be considered statistically insignificant, for example, differences in finger grip height.

  Table 5 Summary of measured weights and dimensions

  The supercritical fluid processing process according to the present invention forms microbubbles on the surface. Such bubbles are drawn out against the mold wall. The feel of these parts is somewhat “rougher” due, at least in part, to one or more of surface finish, cooling, and channel geometry. On the other hand, the inside of the torso and the area gripped by the fingers are more polished. Therefore, these surface parts of the fuselage are less rough. The roughness size is comparable or equivalent to the presence of microbubbles. This slightly “rougher” feel may be a desirable product feature for consumers. Without wishing to be bound by any particular theory, the presence of PTFE improves the “feel” of the surface of the part being produced.

  Referring now to FIGS. 15-18, various parts of the produced part are shown. In particular, FIG. 15 shows an enlarged view of the surface of the applicator fuselage formed by the process of the present invention. FIG. 16 shows the size and distribution of bubbles through a wide angle lens with a highly magnified surface of the fuselage part formed by the process of the present invention. FIG. 17 shows an enlarged view of a petal for a part made in accordance with the present invention. FIG. 18 shows a highly enlarged version of the “fin fin” shape of a part gripped by a finger.

Example 3 Additional Tampon Applicator Body Experiment The same four cavity hot runner molding as in Example 2 above was used to make an additional tampon applicator body. In this particular four cavity molding, two of the cavities are the same as those used for Example 2. The body of the tampon applicator created by these two cavities is a tampon that has a greater absorbency than the regular, average or more widely used tampon ("super absorbent" tampon). Equivalent to. The other two fuselage were made as a slender fuselage. That is, the smaller diameter fuselage typically used for smaller, regular, or less absorbent tampon. The mold is shaped to allow either of these two sets of cavities to be used. But not all four at once. In addition, the two cavities used for the regular or lower absorbency tampon fuselage were polished with diamonds to provide a very smooth polished finish. The cavity for the fuselage corresponding to the more absorbent tampon was polished with diamond. Hundreds of tampon fuselages were made for several condition settings. This condition is roughly similar to that described in Example 2, but the shot size and temperature profiles are slightly different in order to obtain a lower part weight relative to the fuselage in which the microbubbles were generated. Adjusted. Conditions are provided in Table 6 below.

Table 6 Injection Molding Conditions for Example 3 (Note: In all cases, an Arborg 320 injection molding machine was used. It has been described in Example 2. Here, two different cavity settings were used. They were designated as "super" or "slender" types.)

  LDPE (Marlex KN226, Chevron-Phillips) was mixed at the ratio of 19 to 1 with the same green colorant composition.

  Table 7 provides a summary of the data collected for the fuselage made in this example. As you can see, the fuselage formed by the process of microbubbles, whether super (E5 to E8) or slender (E9 to E10), is a conventional injection molding using the same injection molding machine and the same mold. It was lighter in weight than the comparable fuselage of the corresponding condition (C7 or C8) made by The properties recorded here are averages obtained from at least 5 different measurements. An integrated standard error estimate was also recorded here.

  While the weight is clearly different for the fuselage produced by the fine bubbles, the length of the fuselage, the thickness of the petal, the gap of the petal, the inner diameter gripped by the finger, and the height gripped by the finger are conventional It was almost the same as that made by molding. This data uses microbubble technology, even for parts such as very thin parts, parts in tampon applicator petals (which are only 0.012 to 0.014 inches thick), etc. This suggests that it can be made dimensionally stable. This is surprising given what has been taught to date in the prior art related to this technology. More specifically, the tampon applicator body petal against the more absorbent tampon is a machine to soften, shape and seal the petal to encapsulate the fibrous tampon pledget When formed at, the average distance between “petal gaps” or sealed petals remains small and is equivalent to that measured for C7. C7 is formed by conventional injection molding.

  For this example, surface roughness was also measured. These measurements were made using a simple hand operated Federal Marmer (NJ) Pocket Surf II profilometer. These measurements were repeated multiple times (approximately 20 times for each example listed here). The surface roughness for the slender body is lower than for the more absorbent tampon molding. It is probably due to diamond polishing. However, the average value of the fine cell slender roughness (examples E9 to E10) was in fact equal to or slightly lower than that for the conventional molding example (C8) (ie smoother). ). The roughness values for the more absorbent applicator fuselage made by conventional molding (C7) were slightly lower than those for the similarly made fine-bubble fuselage (E5 to E8).

  Table 7 Weight, petal thickness, and other key dimensions for the tampon applicator fuselage in Example 3

  From the above, it can be concluded that it is possible to make a foamed part using LDPE resin by the process of fine foam injection molding. It can also be concluded that the low melting point prevents bubble nucleation, which is the result of an increased activation energy barrier. A high melting point increases the cell population density and decreases the cell size in the microfoam injection molded part. It is caused by lowering the activation energy for nucleation. However, extremely high melting points and large weight loss in parts can result in low melt strength. This is due to bubble coalescence and sometimes larger bubbles. In addition, microfoamed injection molded parts can be produced with a weight loss of up to 20 percent, exhibiting small bubbles that fall in the size range of 5 micrometers to 200 micrometers. Finally, it is possible to make dimensionally stable parts using this microbubble treatment process. Its thickness is as thin as 10 / 1,000 inch.

  Although the invention has been shown and described with reference to specific embodiments, it will be understood that various modifications may be made and certain elements may be replaced by equivalent elements within the scope of the inventive concept. It will be understood by those skilled in the art. In addition, modifications may be made to adopt a particular situation or material within the scope of the inventive concept. Therefore, it is intended that the invention not be limited to the specific embodiments disclosed in the detailed description above. That is, it is intended that the present invention include all specific examples within the scope of the appended claims.

DESCRIPTION OF SYMBOLS 10 ... Apparatus, 12 ... Injection molding part, 14 ... Feed system, 16 ... Hopper, 18 ... Screw transmission part, 20 ... Injection molding part, 40 ... Mold body of tampon applicator, 42 ... Body of tampon applicator, 44 ... projection, 46 ... injection port

Claims (40)

A method of injection molding to produce a microbubble material,
Melting the polymer; and
Mixing the dissolved polymer with a supercritical fluid to produce a single phase polymer gas solution;
Injecting the single phase polymer gas solution into a mold to solidify the polymer;
The pressure drop across the nozzle causes the supercritical fluid to nucleate bubbles, so that the structure of microbubble nucleation in the polymer is whether the polymer is a single phase. How to make it look like. After adding the supercritical fluid and before injecting the single phase polymer gas solution through the nozzle, the temperature of the single phase polymer gas solution is at least 10 degrees higher than the melting point of the polymer. The method of claim 1, further comprising the step of: After adding the supercritical fluid and before injecting the single-phase polymer gas solution through the nozzle, the single-phase polymer gas solution is at least 0 degree above the melting point of the polymer and 20 The method of claim 1, further comprising the step of maintaining the temperature at a temperature that is no greater than degrees. The method according to claim 1, wherein the polymer is LDPE and the temperature falls within a range of 190 degrees Celsius or more and 230 degrees Celsius or less. The method of claim 1, further comprising forming an item in the mold. The method according to claim 5, wherein the total cycle time for forming the article falls within a range of 3 seconds to 100 seconds. The method according to claim 5, wherein a total cycle time for forming the article falls within a range of 3 seconds to 20 seconds. The method according to claim 5, wherein a total cycle time for forming the article falls within a range of 4 seconds to 15 seconds. The method of claim 5, wherein the article to be formed is a tampon applicator body. The method of claim 1, further comprising incorporating a colorant into the polymer. Among antioxidants, lubricants, slip agents, aesthetic enhancing substances, pigments, opacifiers, impact modifiers, fillers, clays, nano-level clays, flame retardants, insulating materials, and / or processing aids The method of claim 1, further comprising incorporating one or more of the following as an additive into the polymer. Solidifying the polymer produces a part having a thickness of at least 0.012 inches;
The method of claim 1, wherein the ratio of flow length to part thickness is at least 200: 1. Comprising a polymer having a structure of fine bubbles produced by nucleated fine bubbles;
The microbubbles are created by diffusing a supercritical fluid into the solution of polymer when the polymer solution is subjected to a drop in pressure. The foam structure according to claim 13, wherein the foam structure is a body of a tampon applicator. The foam structure according to claim 13, further comprising a colorant added to the polymer. Antioxidants, lubricants, slip agents, aesthetic quality enhancing substances, pigments, fillers, impact modifiers, clays, nano-level clays, flame retardants, insulating materials, and processing aids incorporated into the polymer The foam structure according to claim 13, further comprising one or more of the following. The polymer is selected from the group consisting of polyolefins, mixtures of polyolefins with other thermoplastics, polyamides, polycarbonates, polystyrenes, rubbers, polylactides, polyalkanoates, and thermoplastic starch-based resin mixtures. Item 14. A foam structure according to Item 13. The foam structure according to claim 17, wherein the polymer is low-density polyethylene. The foam structure according to claim 13, wherein the supercritical fluid is selected from the group consisting of nitrogen, carbon dioxide, and mixtures thereof. The foam structure according to claim 13, wherein the fluid that exceeds the criticality is nitrogen that falls within a range of 0.05 weight percent or more and 1 weight percent or less. The foam structure according to claim 13, wherein the fluid that exceeds the criticality is nitrogen that falls within a range of 0.15 weight percent or more and 0.45 weight percent or less. The foam structure according to claim 13, wherein the thickness of the component is 0.01 inch or more. 19. The foam structure of claim 18, further comprising a mixture of at least 70 percent low density polyethylene and at least one of PTFE and PFA falling in the range of 0.1 percent to 20 percent. A feminine hygiene device comprising a foamed polymer having a microbubble structure produced by stirring a supercritical fluid in a polymer melt. The polymer is selected from the group consisting of polyolefins, mixtures of polyolefins with other thermoplastics, polyamides, polypropylenes, polycarbonates, polystyrenes, rubbers, polylactides, polyalkanoates, and mixtures of thermoplastic starch-based resins. A feminine hygiene device according to claim 24. The feminine hygiene device according to claim 24, wherein the polymer is low density polyethylene. The feminine hygiene device according to claim 24, wherein the feminine hygiene device is a body of a tampon applicator. 28. The feminine hygiene device of claim 27, wherein the thickness of the component is at least 0.01 inches or more. 25. The female satellite apparatus according to claim 24, wherein the average size of the bubbles of the fine bubble structure falls within a range of 5 micrometers or more and 200 micrometers or less. 25. A feminine hygiene device according to claim 24, wherein the device is defined by a wall surface having a thickness in the range of 0.003 inches to 0.10 inches. Colorants, antioxidants, lubricants, slip agents, aesthetic enhancing substances, pigments, dyes, opacifiers, impact modifiers, fillers, clays, nano-level clays, flame retardants incorporated into the polymer The feminine hygiene device according to claim 24, further comprising one or more of processing aids. 27. A feminine hygiene device according to claim 26, further comprising a mixture of at least 80 percent low density polyethylene and at least one of PTFE and PFA falling in the range of 0.1 percent to 10 percent. A method of injection molding a feminine hygiene device,
Supplying a polymer as a base for the state of small particles;
Adding the base polymer to the screw transmission section;
Adding a supercritical gas to the screw transmission section;
Combining the base polymer and the supercritical gas;
Injecting the combined base polymer and supercritical gas into a mold to provide a shaped feminine hygiene device having a matrix of a substantially continuous thermoplastic phase; A method comprising: The step of supplying the base polymer includes a thermoplastic material, a colorant, a lubricant, a slip agent, a filler, a clay, a nano-level clay, an opacifier, a pigment, an impact modifier, a flame retardant, and an insulating material. And a method of mixing at least one additive selected from the group consisting of processing aids. 34. The method of claim 33, wherein adding the base polymer to the screw transmission portion comprises adding the base polymer through a hopper. 34. The method of claim 33, further comprising heating the base polymer applied to the screw transmission portion. 37. The method of claim 36, wherein heating the base polymer comprises deforming the base polymer using a plasticizing screw. The method of claim 36, wherein heating the base polymer comprises heating the screw transmission portion using an electrical heat source. 34. Injecting the combined base polymer and supercritical gas into a mold further comprises providing a hollow core into the molded feminine hygiene device. the method of. A composite used in feminine hygiene products,
An amount of low density polyethylene in the range of 94 weight percent or more and 97 weight percent or less;
A colorant in an amount of 4 weight percent or less;
Oleamide in an amount of 2 weight percent or less, and
The feminine hygiene product is a composite manufactured using a microfoam injection molding process.